Characterizations of power loads on divertor targets for type-I, compound and small ELMs in the EAST superconducting tokamak: Paper

L. Wang, G.S. Xu, H.Y. Guo, H.Q. Wang, S.C. Liu, K.F. Gan, X.Z. Gong, Y. Liang, Ning Yan, L. Chen, J.B. Liu, W. Zhang, R. Chen, L.M. Shao, H. Xiong, J.P. Qian, B. Shen, G.J. Liu, R. Ding, X.J. ZhangC.M. Qin, S. Ding, L.Y. Xiang, G.H. Hu, Z.W. Wu, G.N. Luo, J.L. Chen, L.Q. Hu, X. Gao, B.N. Wan, J.G. Li

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The Experimental Advanced Superconducting Tokamak (EAST) has recently achieved a variety of H-mode regimes with different edge-localized mode (ELM) dynamics, including type-I ELMs, compound ELMs, which are manifested by the onset of a large spike followed by a sequence of small spikes on Dα emissions, usual type-III ELMs, and very small ELMs. This newly observed very small ELMy H-mode appears to be similar to the type-II ELMy H-mode, with higher repetition frequency (∼1 kHz) and lower amplitude than the type-III ELMy H-mode, exhibiting an intermediate confinement level between type-I and type-III ELMy H-modes. The energy loss and divertor power load are systematically characterized for these different ELMy H-modes to provide a physics basis for the next-step high-power long-pulse operations in EAST. Both type-I and compound ELMs exhibit good confinement (H98(y,2) ∼ 1). A significant loss of the plasma stored energy occurs at the onset of type-I ELMs (∼8%) and compound ELMs (∼5%), while no noticeable change in the plasma stored energy is observed for the small ELMs, including both type-III ELMs and very small ELMs. The peak heat flux on divertor targets for type-I ELMs currently achieved in EAST is about 10 MW m−2, as determined from the divertor-embedded triple Langmuir probe system with high time resolution. As expected, type-III ELMs lead to much smaller divertor power loads with a peak heat flux of about 2 MW m−2. Peak power loads for compound ELMs are between those for type-I and type-III ELMs. It is remarkable that the new very small ELMy H-modes exhibit even lower target power deposition than type-III ELMs, with the peak heat flux generally below 1 MW m−2. These very small ELMs are usually accompanied by broadband fluctuations with frequencies ranging from 20 to 50 kHz, which may promote particle and power exhaust throughout the very small ELMy H-mode regime.
Original languageEnglish
JournalNuclear Fusion
Issue number7
Pages (from-to)073028
Number of pages9
Publication statusPublished - 2013

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